1. Field of the Invention
This invention relates to an exit device having deadbolt as its securing member, and more particularly to an exit device including a press bar on the inside of a door. When the press bar is pushed, it retracts the securing member so that the door can be opened.
2. Description of Related Art Including Information Disclosed Under .sctn..sctn.1.97 to 1.99
State and federal codes have required that exit doors for public buildings be equipped with exit devices so that occupants exiting a building can press a panic bar or press bar to actuate the latchbolt of the door. Such pressing--as opposed to turning a handle or knob--is natural, particularly with persons escaping a building in a panic situation.
Devices of this sort are well known, an example being disclosed by the U.S. Pat. No. 4,796,931 to George E. Heid which issued Jan. 10, 1989, and is assigned to my assignee. The Heid patent describes the linkages between the press bar and a latchbolt which is pivotally mounted adjacent the open end of the door.
Such structures have been designed to function under extreme conditions--the stampede of panicking adults toward the exit in a smoke-filled auditorium, for instance. A herd of such persons arriving at a closed door can exert a great outward force on the door and the exit device. A standard exit device test by Underwriters Laboratories replicating such conditions involves exerting a horizontal outward force of 250 pounds against a closed door to test the exit device installed thereon. A further test during the application of the 250 pound force described above, requires that the press bar operate at a force of less than 50 lbs. This press bar force augments the 250 pound force mentioned above so that the total outward force on the latch can be up to 300 pounds. To counter this enormous force in the opening direction, designers of exit devices have avoided the preferred more-secure reciprocating deadbolt with its high lateral friction and have adopted pivoted latchbolts. Such latchbolts have strike-engaging latching surfaces which are curved or beveled, thereby easing the resistance to retraction in the keeper as the door and exit device are pressed outward, but exerting lateral forces which separate the door and the frame thereby reducing door security.
In other words, while rectangular or square deadbolts, as known in the lock industry, offer better strength and security, they require a substantial force to slide them to retracted position under the above extreme conditions because of the large perpendicular forces acting on the bearing surfaces. Because failure of an exit device to open could be catastrophic, the preference for square or rectangular deadbolt-type locking members has been cast aside for the easier-opening pivoted latchbolt described above. As a result, doors equipped with pivoted latchbolts have been more vulnerable to vandalism. Also, in fire situations in which enormous heat has warped the door and frame, pivoted latchbolts have been known to foil and pop open during fire tests.